Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $66.92   9.838%   $73.5036   $73.50   $73.50   $73.50  
  Purchase #2 $168.77   12.165%   $189.3009   $189.30   $189.30   $189.30  
  Purchase #3 $85.67   13.681%   $97.3905   $97.39   $97.40   $97.40  
  Purchase #4 $157.99   12.707%   $178.0658   $178.07   $178.05   $178.10  
  Purchase #5 $203.61   10.793%   $225.5856   $225.59   $225.60   $225.60  
  Purchase #6 $191.86   13.658%   $218.0642   $218.06   $218.05   $218.10  
  Purchase #7 $79.94   4.360%   $83.4254   $83.43   $83.45   $83.40  
  7 purchase totals = $954.76       $1,065.3360   $1,065.34   $1,065.35   $1,065.40